Valid Saturday December 10, 2016 to Wednesday December 21, 2016
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EST December 07 2016Synopsis
: Arctic high pressure is forecast
to expand south and east from the northern Rockies and northern Great Plains
from Dec 10 to 14. A low pressure system is expected to precede the arctic
front and track across the upper Midwest this weekend. Multiple waves of
surface low pressure are expected to push inland into the western U.S. during
the next week to ten days. A strong area of upper-level high pressure is
expected to remain anchored over the Bering Sea with arctic high pressure
extending from northeast Alaska into the east-central continental U.S. during
Detailed Summary For Saturday
December 10 - Wednesday December 14:
- Much below-normal temperatures for the
southeastern U.S., Sat, Dec 10.
- Much below-normal temperatures for parts of the northern Great Plains,
northern Rockies, and Washington, Sat-Wed, Dec 10-14.
- Much below-normal temperatures shifting southeast across the Great Plains
and Midwest, Tue-Wed, Dec 13-14.
- Locally heavy snow for parts of South Dakota, the upper Midwest, and Great
Lakes, Sat, Dec 10.
- Heavy, lake-effect snow downwind of the Great Lakes, Tue-Thu, Dec 13-15.
- Periods of heavy precipitation (rain and high-elevation snow) for parts of
the Pacific Northwest and northern California, Sat-Thu, Dec 10-15.
- Periods of heavy snow for parts of the northern Great Basin, Pacific
Northwest, and northern/central Rockies, Sat-Thu, Dec 10-15.
- Much below normal temperatures across the Alaska Panhandle, Sat-Wed, Dec
- A slight risk of much below-normal temperatures for much of the continental
U.S. and Alaska Panhandle, Thu-Wed, Dec 15-21.
- A moderate risk of much below-normal temperatures for parts of the Ohio
Valley, mid-Atlantic, and Northeast, Thu-Fri, Dec 15-16.
- A moderate risk of much below-normal temperatures for parts of the northern
Rockies, Great Plains, Midwest, Great Lakes, and Alaska Panhandle, Thu-Sun, Dec
- A high risk of much below-normal temperatures for parts of the northern
Rockies, northern/central Great Plains, and upper Mississippi Valley, Thu-Sun,
- Severe drought across parts of the eastern U.S., Great Plains, Missouri
River Valley, central Rockies, Intermountain West, California and Hawaii.
Surface high pressure centered over
the southern Appalachians is forecast to result in much below-normal
temperatures (departures of 12 degrees F or more) across the Southeast on Dec
10. Hard freezes are expected as far south as the Florida Panhandle on Saturday
A surface low is forecast to develop across the north-central high Plains
by Saturday, Dec 10 and then track rapidly east to the Great Lakes. Moderate to
locally heavy snow (4 inches or more) is expected to accompany this surface low
as it tracks from South Dakota east to the Great Lakes. The GFS ensemble mean
indicates precipitation amounts of 0.25 to 0.50 inches (liquid equivalent) in
the outlined area for heavy snow.
Arctic high pressure is likely to result in much below-normal temperatures
across the northern Great Plains, northern Rockies, and northeast Washington
state through at least Dec 14. Model guidance remains consistent that this
arctic surface high expands southeast across the Great Plains and east-central
U.S. next week. The much below-normal temperature hazard is posted for areas
where the minimum temperatures are forecast to average more than 12 degrees F
below normal. The largest negative anomalies of 20 to 30 degrees F are forecast
across the northern high Plains where minimum temperatures could fall to around
-20 degrees F from Dec 10 to 14. Dangerous wind chills of -20 to -40 degrees F
are also likely to accompany this arctic outbreak across the north-central U.S.
Strong cold air advection, following the passage of an arctic front, is
forecast to renew heavy lake-effect snow downwind of the Great Lakes, beginning
on Dec 13. Total snowfall amounts are expected to exceed one foot in the most
favored snow belts south and east of the Great Lakes from Dec 13 to 15.
Waves of low pressure are forecast to bring periods of heavy rain and
high-elevation snow (total amounts of more than 5 inches, liquid equivalent) to
parts of the Pacific Northwest and northern California from Dec 10 to 14. There
remains an increased risk of freezing rain across the interior Pacific
Northwest where precipitation coincides with the shallow arctic air. Elsewhere,
periods of heavy snow (more than 6 inches per 24 hours) are forecast across the
interior West as individual shortwave troughs with enhanced Pacific moisture
push inland from Dec 10 to 14.
Arctic high pressure over western Canada and anomalous easterly flow is
expected to result in much below-normal temperatures across the Alaska
Panhandle from Dec 10 to 14. The 6Z GFS ensemble mean generally indicates that
temperatures will average 16 degrees F or greater below normal across the
Alaska Panhandle. For Thursday December 15 -
Wednesday December 21:
Ensemble means agree that anomalous ridging aloft
persists across the Bering Sea and western Alaska through Week-2. Much
below-normal temperatures are likely to affect the northern half of the
continental U.S. and the Alaska Panhandle. The slight, moderate, and high risk
of much below-normal temperatures is based generally on areas where the GEFS
reforecast tool indicates daily minimum temperatures with a 20, 40, or 60
percent chance, respectively, of falling below the 15th percentile comparted to
climatology. The 6Z GFS ensemble mean indicates temperatures averaging as much
as 25 degrees F below normal across the northern Great Plains and upper
Mississippi Valley early in Week-2. The GFS model continues to offer a colder
solution for the Pacific Northwest compared to the ECMWF model.
Based on good model agreement and consistency, the heavy precipitation
(rain and high-elevation snow) for the southern Cascades and northern Sierra
mountains along with heavy snow across the interior West is maintained through
Dec 15. Also, cold air advection is expected to prolong the lake-effect snow
event through Dec 15. Although the potential exists for winter weather hazards
across the east-central U.S. during Week-2, the development and subsequent
tracks of any low pressure systems remain uncertain.
According to the latest U.S. Drought Monitor (USDM) valid on November 29,
the coverage of severe or greater drought for the CONUS decreased nearly a half
percent to 16.6%. Improvements were noted for portions of the Lower Mississippi
Valley and New York state. While the most recent USDM shows deterioration of
drought conditions in the Southeast, rains following the latest release may
yield improvement for the next publication.
Click here to see a display of the GFS Ensemble Forecasts
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.